Rheostat unit



P 28, 1954 L. J. PARKINSON ETAL RHEOSTAT UNIT Filed May 18, 1953 J Inventors Leland-J. Parkinson,

Char les H.5nyder,

rv ttor-ney.

Patented Sept. 28, 1954 g i i i armos'rar UNIT York Application May 18, 1953, Serial No. 355,836

(Cl. fill-48) 4 Claims.

This invention relates to rheostats and more particularly to the combination of a plurality of rhcostats into a single operating unit in such a manner that their operation in a definite sequence is assured.

One application in which the invention is particularly useful is that of an adjustable voltage motor control system in which the motor is supplied from an adjustable voltage generator. In such application, the motor field is maintained at full strength while the motor is being accelerated from rest to basic speed by increasing the voltage supplied to its armature from zero to full value. This is accomplished by increasing the held of the generator from zero to full value.

The speed of the motor may be increased above its basic value by weakening the field strength of the motor. Thus to accelerate the motor from standstill to a speed within the field weakening range, the generator field rheostat and the motor field rheostat must be operated in proper seuence, i. e., the generator field rheostat must be operated from the resistance all in position to the resistance all out position while the motor field rheostat is maintained in the resistance all out position. Then the motor field rheostat must be operated from the resistance all out position toward the resistance all in position while the generator field rheostat is maintained in the resistance all out position.

In the sequential operation of the two rheostats in such a system it is desirable that both rheostats may be operated by manipulation of a single handle. Accordingly a further object of the invention is the provision of a rheostatic unit comprising a plurality of rheostats which are operated in the desired sequence by means of a single handle and in which the contact arms of the rheostats are rotated through a complete revolution and in proper sequence in response to one complete revolution of the control of the operating handle.

Heretofore, various solutions have been devised for achieving this result such, for example, as the inclusion of segmental gears between the operating handle and the contact arms of the rheostats. This construction however has its disadvantages. Segmental gears are not standard articles of manufacture but must be specially milled and machined from standard gears. These milling and machining operations add greatly to the cost of the gears. Another disadvantage of the segmental gear construction is that great care must be taken in the initial positioning of the segmental gears on their shafts with respect to the positions of the contact arms of the several rheostats and the handle pointer in order that the position of the pointer may provide a correct indication of the positions of the contact arms. This results in a costly assembly operation. Thus, a further object of the invention is the provision of an inexpensive unit in which two or'more rheostats are combined and in which a single complete rotation of the operating handle produces a complete rotation of the contact arm of each of the rheostats in proper sequence. A still further object of the invention is the provision of a plural rheostat unit of the character described in which the driving connections between the operating handle and the contact arms consists of low cost standard parts which may be assembled with very little skill.

Another disadvantage of the segmental gear construction is that the contact arm of each of the rheostats becomes disconnected from the operating handle at the point in the operation at which the drive from the handle is transferred from one contact arm to another with the result that the disconnected contact arm is not locked or held in the initial position or terminal position to which it has been rotated by the operating handle. Consequently, when installed on or in close proximity to machinery subject to substantial vibration, the disconnected contact arm may be Worked loose by the transmitted vibration and moved from the position to which it was rotated by the handle to some other position. Such accidental displacement of the free contact arm has several undesirable results. (1) The position of the handle pointer is no longer a true indication of the relative positions of the contact arms of the several rheostats of the unit. (2) To restore the correct relative positions of the contact arms and handle pointer it is necessary partially to disassemble the unit. (3) When applied to an adjustable voltage motor control systern, such accidental displacement of the contact arm of the generator field rheostat from its full voltage position prevents development of full generator voltage until the unit is disassembled and the correct relationship is reestablished. Similarly such accidental displacement of the contact arm of the motor field rheostat from its minimum resistance position prevents increase of the motor field to full strength and thus reduces its starting torque. In the one case, the position of the handle pointer is not a correct indication of the generator field strength and in the other case it is not a correct indication of the motor field strength. In neither case is it a correct indication of the motor speed. Accordingly, a further object of this invention is the provision of a plural rheostat unit of the character described in which the contact arms of the several rheostats are at all times mechanically connected with the operating handle and in which means are provided for locking each contact arm against accidental displacement from the position at which transfer of the handle drive from one contact arm to another is accomplished.

In carrying the invention into effect in one form thereof a plurality of plate type rheostats are combined with an operating handle to form a unit in which a complete rotation from an initial position to a terminal position of the contact arm of each of the rheostats in a desired sequence is produced in response to one complete rotation of the operating handle. The input member of a mechanical differential device is mechanically connected to the operating handle, and the two output members of the differential device are respectively connected to the contact arms of the rheostats. During a rotation of the operating handle to rotate one of the contact arms, a stop means serves to lock the stationary contact arm against rotation or accidental displacement from its position at the point at which the drive from the operating handle is transferred from one contact on to the other.

For a better and more complete understanding of the invention reference should now be had to the following specification and to the accompanying drawing of which Fig. 1 is a view in side elevation partly in section on the line l-l of Fig. 2 of the combined operating handle and sequencing means, Fig. 2 is a view in front elevation with certain portions broken away, of the combined rheostats with operating and sequencing means, and Figs. 3, 4 and 5 are front elevational views of details of the sequencing mechanism which illustrate different stages of the sequencing operation.

Referring now to the drawing a rheostatic unit comprises a plurality of rheostats l and 2 combined with an operating handle 3 and a sequencing mechanism 4. Since the rheostats l and 2 are substantially identical, only the rheostat l is described in detail. The rheostat 5 comprises a plate and cover assembly 5 within which is mounted a wiring plate 6 which is made of a I suitable heat resisting insulation material. The resistor 6a is wound on the wiring plate in a toroidal manner. A plurality of stationary contacts T are welded to the resistor at suitable intervals and each is provided at its inner end with a suitable stud or button la. A bearing hub 8 is centrally mounted in the plate and cover assembly and secured thereto, by means of cap screws 9, is a stop washer In which is provided with a stop lug Illa which extends radially from the lockwasher beyond its circular periphery. The cap screws 9 may be loosened and the washer adjusted so that the lug Illa occupies any desired peripheral position in which it may be secured by again tightening the cap screws.

An antifriction bearing II is molded in the bearing hub 8. Preferably it is made with a suitable long life antifriction material such for example as copper graphite. A shaft [2 is journaled for rotation in the bearing II and an L-shaped stop member 13 is welded to the shaft 12 at one end thereof. To the opposite end of the shaft [2 is keyed a brush support Ma and contact arm 14 on which are mounted two brushes [5 and IS. The brush [5 is illustrated as making contact with the stationary contact buttons la. It will be understood that it makes contact with these buttons in succession as the contact arm is rotated. The brush I8 is illustrated as making contact with a collector ring I! which is mounted on the bearing hub and which is electrically connected by means of a suitable connector l8 to a central terminal l9. Outside terminals and 20a are respectively connected to opposite ends of the toroidal resistor which is wound on the wiring plate.

The shaft [2 which carries the contact arm I4 is connected to a shaft [2a by means of a coupling disk assembly which extends through a hollow shaft 40 in the front rheostat 2. The sequencing mechanism 4 is mounted upon a cover assembly plate 2!. This plate is secured to the plate and cover assembly of the front rheostat 2 by suitable fastening means (not shown) and is separated therefrom by suitable spacers 22 and 23. A bearing '24 is centrally mounted in the plate 2| and is lined with a bushing within which is journaled for rotation of a shaft 25, to the projecting end of which the operating handle 3 is keyed. The right-hand end of the shaft 25 is machined to a reduced diameter, and the left-hand end of the shaft lZa which drives the contact arm of the rear rheostat is hollowed to receive the reduced diameter portion of shaft 25 and to act as a bearing within which it is journaled for rotation. Keyed to the shaft 25 is an arm 26 which at its extremities is provided with two stub shafts 2i and 28 upon which are rotatably mounted planet gears 29 and 30. As shown, the planet gear 23 in reality comprises two gears of which the first 29a is a pinion gear and the second gear 291) is a spur gear. The gears 29a and 2% are either formed integrally with each other as shown or are separate gears keyed to each other. Similarly the planet gear 30 comprises a spur gear 830 and a pinion gear 301). The two spur gears 22a and 39a of the planet gears mesh with a sun gear 3'[ which is keyed to the shaft Pia. Meshing with the pinion gears 29b and 39b is an annular internal gear 32. Secured to the internal gear 32 by suitable fastening means such for example as machine screws 33 and 33a is a disk and coupling assembly 34. This disk and coupling assembly is provided with a stop arm 35 which is provided with a cam surface 35a. Keyed to the shaft 12a is a second stop arm 35 which is also provided with a cam surface 36a.

Secured to the plate 34 of the disk. and coupling assembly is a coupling strap 31. It may be fastened to the plate 84 by welding or by any other suitable fastening means. A couplin disk 38 couples the coupling strap 3! to a coupling bar 39. This couplin bar 39 is connected by means of a hollow shaft 46 to the contact arm (not shown) of the front rheostat 2. A locking means 4! is secured to the cover plate 2! by suitable fastening means such for example as bolts 32 and 43. This locking means comprises a pair of L.-shaped stop levers 44 and which are pivotally mounted for rotation on the bolts 42 and 43 respectively. The upright ends of these L-shaped stop levers are connected together by means of a tension spring 46 which tends to rotate the stop lever 44 in a counterclockwise direction and a stop lever 45 in a clockwise direction.

The parts are assembled so that when the handle 3 and its handle pointer 3a are in the extreme counterclockwise position, the contact arms of the rheostats l and 2 will be in correspending extreme positions and the stop arm 35 will be in the position in which it is illustrated in engagement with the horizontal portion of lever and prevented from clockwise rotation thereby. The stop arm as will also be in its extreme counterclockwise position as illustrated.

With the foregoing understanding of the elements and their organization, the operation of the unit will readily be understood from the following dc-tailed description: As the handle 3 is rotated in a clockwise direction it rotates the planet gear arm 26 carrying with it the planet gears and causing them to rotate about the axis of the shaft and about their own axes. This rotation of the planet gears tends to cause the output gears i. e., the annular internal gear 32 and the sun gear 3! to rotate. However, at this point in the operation the internal gear 32 is res-trained from rotation because it is secured to the plate B l of which the stop arm 35 is at the moment engaged by the horizontal portion of he stop lever as illustrated in Fig. 3.

Consequently, the rotation of the handle 3 causes the sun gear 3! to rotate and thus to rotate the shaft to which is attached the arm of the rear rheostat i. The ratio of z. s of the differential gear train is such the handle 3 has been rotated through he 22:; will have rotated through substantially 35 and the L-shaped stop arm it of the rear rheostat will have been rotated up the stop lug lilo so that further rotation shaft 52a of the contact arm of the rear is prevented. the end of this 360 of rotation of the surface of the stop arm 36 iereto engages the horizontal .e stop lever all as illustrated in Fig. ind it so that it no longer restrains the stop arm and the disk and coupling assembly Thus continued rotation of now causes the planet gears 29 and -otato the annular internal gear 3! in a clockwise direction. This results in rotating the disk and the hollow shaft so which is secured to the contact arm of the front rheo- 9' Shortly after the beginning of this clockrotation of the disk and coupling assembly cam surface 35a of the stop arm 35 passes out from under eath the right-hand edge of the horizontal portion of the stop lever 55 which it has been holding in the released position. Consequently the spring 46 rotates the stop lever in a counterclockwise direction so that it drops behind the trailing edge of the stop lever 36 and thus prevents counterclockwise rotation of the stop lever 36, as illustrated in Fig. 5.

Continued rotation of the handle 3 rotates the contact arm of the front rheostat 1 until at the completion of 360 rotation of the handle the contact arm of the rheostat I has also rotated through 360 and is now in an extreme position.

The counterclockwise rotation of the handle 3 from its extreme clockwise position results in a similar but reverse operation. At the end of 180 of counterclockwise rotation, the contact arm of front rheostat has been rotated to its initial pee ion by the counterclockwise rotation of the isk and coupling assembly 34. Near the end of first 180 counterclockwise rotation of the -Cle 3, the cam surface 35a of the stop arm 35 -gages the horizontal portion of the stop lever and raises it against the tension of the spring and thus releases the stop arm 36 so that it is free to rotate in response to further counterdb re 0 m on 3 clockwise rotation of the handle. Simultaneously, the L-shaped stop arm 39 on the front rheostat 2 comes up against its extreme counterclockwise stop and is prevented from further rotation in the counterclockwise direction.

Continued rotation of the handle in the counterclockwise direction causes the stop arm 35 to pass out from beneath the horizontal portion of the stop lever 3 which in response to the tension of the spring 4% is rotated to the position in which it is illustrated in Figs. 2 and 3 of the drawing to prevent unintended clockwise rotation Of the stop arm 35 and the contact arm of the fcnt rheostat 2 to which it is connected. As the c anterciockwise rotation of the handle 3 con tinucs, the contact arm of the rear rheostat i is rotated in a counterclockwise direction toward its l al position. When the handle pointer handle reaches its zero position, the conof tact arm of the rear rheostat 2 is in its extreme initial position and the stop arm S6 is also in its extreme counterclockwise position in which it is illustrated in the drawing.

It will be noted that the contact arms of the rheostats are never mechanically disconnected from the operating handle 3. The coaction between the stop arms 35 and 36 and the stop levers id and i5 insures that the contact arms of the rheostats are locked in the positions which they have come to occupy at the instant that the drive from the operating handle is transferred from one contact arm to the other. Thus there can be no free wheeling of the contact arms and consequently they cannot be moved from their positions by vibration of the machinery with which the unit is used or upon which it is mounted regardless of how severe the vibration be. Consequently the positional relationshi between the contact arms cannot he accidentally changed and the position of the handle pointer is always a correct indication of the relative positions of the contact arms.

Although in accordance with the provision of the patent statutes, this invention has been de scribed as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the description and drawings are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of the invention or from the scope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A rheostatic unit comprising a plurality of rheostats each comprising a contact arm having a zero position and a shaft mounting said contact arm for rotation, a rheostat operating member having an off position, a mechanical differential device having an input member connected to be driven by said operating member, a first output member connected to drive the shaft of a first of said rheostats and a second output member connected to drive the shaft of a second of said rheostats, stop means for restraining said second output member against rotation in one direction and said first output member against rotation in the opposite direction thereby to provide for rotation of the contact arm of said first rheostat in response to rotation of said operating member from said off position, a member driven by said first output member and provided with a cam surface for actuating said stop means at the end of a complete rotation of the contact arm of said first rheostat from its zero position to release said second output member to provide for rotation of the contact arm of said second rheostat in response to continued rotation of said operating member in the same direction.

2. A rheostatic unit comprising a plurality of rheostats each provided with a contact arm having a terminal position and mounted for rotation, a rheostat operating member, a mechanical difierential device having an input member connected to be driven by said operating member, a first output member connected to drive the contact arm of a first of said rheostats, a second output member connected to drive the contact arm of a second of said rheostats, stop means for restraining said first output member against rotation in one direction and said second output member against rotation in the opposite direction to provide for rotation of the contact arm of said first rheostat from its terminal position in response to rotation of said operating member from said off position, a member driven by said first output member for actuating said stop means at the end of a complete rotation of the contact arm of said first rheostat from its terminal position to release said second output member to provide for rotation of the contact arm of said second rheostat in response to continued rotation of said operating member in the same direction.

3. A rheostatic unit comprising a plurality of rheostats each provided with a contact arm having a terminal position and mounted for rotation, a rheostat operating member, a mechanical differential device having an input member connected to be driven by said operating member, a first output member connected to drive the contact arm of a first of said rheostats, a second output member connected to drive the contact arm of a second of said rheostats, stop means for restraining said first output member against rotation in one direction and said second output member against rotation in the opposite direction to provide for rotation of the contact arm or" said first rheostat from its terminal position in response to rotation of said operating member from said off position, a stop arm driven by said first output member for actuating said stop means at the end of a complete rotation of the contact arm of said first rheostat from its terminal position to release said second output member to provide for rotation of the contact arm of said second rheostat from its terminal position in response to continued rotation of said operating member in the same direction, and a second stop arm driven by said second output member for actuating said stop means upon return of the contact arm of said second rheostat to its terminal position in response to reverse rotation of said operating member to actuate said stop means to release said first output member to provide for return of the contact arm of said first rheostat to its terminal position in response to continued reverse rotation of said operating member.

4. A rheostatic unit comprising a plurality of rheostats each provided with a contact arm having a terminal position and mounted for rotation, a rheostat operating member, a mechanical difierential device having an input member connected to be driven by said operating member, a first output member connected to drive the con tact arm of a first of said rheostats, and a second output member connected to drive the operating arm of a second of said rheostats, a first spring biased stop lever for restraining said second out put member against rotation in one direction to provide for rotation of the contact arm of said first rheostat from its terminal position in response to rotation of said operating member in one direction, a stop arm driven by said first output member for actuating said stop lever at the end of a complete rotation of the contact arm of said first rheostat from its terminal position to release said second output member to provide for rotation of the contact arm of said second rheostat in response to continued rotation of said operating member in the same direction, a second spring biased stop lever for engaging said stop arm to restrain said first output member from rotation in the reverse direction to provide for return of the contact arm of said second rheostat to its terminal position in response to reverse rotation of said operating member, and a second stop arm mounted on said first output member for actuating said second stop lever upon return of the contact arm of said second rheostat to its terminal position to release said first stop arm to provide for return of the contact arm of said first rheostat to its terminal position in response to continued rotation of said operating arm in the reverse direction.

No references cited. 

